There are two main types of water reuse projects:

In the United States and other countries, purple pipes are used to distinguish nonpotable distribution systems, helping to prevent cross-connections.

Nonpotable reuse projects treat wastewater for specific purposes other than drinking, such as industrial uses, agriculture, or landscape irrigation. Nonpotable reuse could also include the use of reclaimed water to create recreational lakes or to build or replenish wetlands that support wildlife.

Potable reuse projects use highly treated reclaimed wastewater to augment a water supply that is used for drinking and all other purposes.

Nonpotable Reuse

In St. Petersburg, Florida, reclaimed water is used for nonpotable purposes such as landscape irrigation.Nonpotable Reuse

Nonpotable reuse systems typically have lower water quality objectives than potable systems, and the level of treatment varies depending on the end use. Nonpotable reuse usually requires a “dual distribution system”—separate systems of pipes for distributing potable and -nonpotable water. Depending on the extent of a community’s nonpotable water distribution system, -nonpotable reclaimed water can be used for flushing toilets, watering parks or residential lawns, supplying fire hydrants, washing cars and streets, filling decorative fountains, and many other purposes.

The country’s oldest dual distribution system is in Grand Canyon Village, Arizona, which has been using reclaimed water for nonpotable uses since 1926. In St. Petersburg, Florida, which began building a large-scale nonpotable reuse system in the 1970s, reclaimed water now satisfies about 40 percent of the city’s total water demand, with many of the city’s parks, schools, golf courses, residential lawns, fire hydrants, and commercial buildings drawing reclaimed water for non-potable uses.

Reclaimed water at the Orange County, California, Groundwater Replenishment System is treated by reverse osmosis (left) and other advanced treatment systems before it is either injected into potable water supply aquifers or allowed to percolate into groundwater through infiltration basins (right). Producing 70 million gallons of potable water per day, the project is the country’s largest potable water reuse system. It uses wastewater that would otherwise have been discharged into the Pacific Ocean.

Potable Reuse

Potable reuse systems use advanced treatment processes to remove contaminants from wastewater so that it meets drinking water standards and other appropriate water quality -objectives. Typically, the highly treated reclaimed water is then released into a surface water body or aquifer (also called an environmental buffer) before being withdrawn, further treated, blended with other conventional water supply sources, and piped to homes and buildings.

Potable water reuse systems have existed in the United States for 50 years. The Sanitation Districts of Los Angeles County, for example, have been using highly treated reclaimed water to augment Southern California’s potable water supply since 1962. Similar systems are in place in other locations in California and in other states, including Virginia, Texas, Georgia, Arizona, and Colorado. About half the nation’s potable reuse systems have come on line during the past decade.

De Facto Reuse

Throughout the United States, some communities may already be reusing wastewater without even realizing it. De facto reuse occurs when a community draws water from a river or -reservoir that includes wastewater from upstream communities. De facto reuse is quite common, although it has not been systematically analyzed in the United States in more than 30 years. Since last assessed, de facto reuse has likely increased as expanding cities now discharge more treated wastewater into water sources used by downstream communities. De facto reuse is particularly pronounced in dry periods, when natural water supplies are reduced and wastewater makes up a larger proportion of the water flow.

Click here to see an animated illustration showing the processes involved in urban de facto water reuse.

According to 2008 estimates, the United States reuses a greater volume of water than any other country (shown here in billions of gallons per day, BGD), and it is ranked thirteenth among countries by per capita water reuse. Qatar and Israel have the highest water reuse per capita. Data from Jiménez and Asano (2008).